Several problems arise when hard soldering or brazing aluminum materials using a brazing or solder material of the prior art. For example, the outer surface of the aluminum material becomes covered with an oxide skin, which must be removed immediately before wetting the aluminum material with the solder, in order to achieve an acceptable solder joint. Due to the relatively large affinity of the aluminum to oxygen under normal environmental conditions, the oxide skin is very quickly re-formed even after it has been removed. Other problems in soldering such aluminum materials result due to the very low melting temperature of the materials. For example, the solidus temperature of the base material, which cannot be reached or exceeded during the soldering process, is about 579.degree. C.
A typical commercially available solder material, which is known under the designation L-AlSi12, consists of an aluminum-based alloy containing approximately 12% of silicon. This known solder material has a working temperature of 590.degree. C. for example, and is therefore not suitable for many applications. Furthermore, this known solder material must be used with a flux for removing the oxide skin that forms on the aluminum components.
Other solder materials are known for carrying out fluxless hard soldering. Such known solder materials also consist of an aluminum-based alloy containing silicon and germanium as further alloying elements. Such solder materials are used for the fluxless hard soldering of aluminum components having a solidus temperature over 600.degree. C. in a vacuum or in a protective or inert gas environment. By evaporating low-melting-point metals having a greater oxygen affinity than the aluminum, the oxide skin on the surface of the aluminum components is removed in a chemical manner by a reduction reaction, that is to say, the getter effect of these low-melting-point metals is utilized to remove the oxide skin. A material that is typically used for this purpose is magnesium, which is evaporated within the inner chamber of the soldering oven. The soldering process is thereby carried out under a high vacuum at pressures of 10.sup.-3 to 10.sup.-4 hPa.
It is further known to carry out fluxless hard soldering of aluminum under a protective or inert gas with a dew point of less than -60.degree. C. and an oxygen content of less than 10 ppm, or in a vacuum of 10.sup.-2 to 10.sup.-3 hPa. In such a known process, the solder material must include wetting enhancing elements such as antimony, barium, beryllium, strontium and/or bismuth. Furthermore, it is usually necessary to carry out a corrosive degreasing step to clean the components to be joined before carrying out the soldering process.
U.S. Pat. No. 5,158,621 (Das et al.) issued Oct. 27, 1992 and U.S. Pat. No. 5,286,314 (Das et al.) issued Feb. 15, 1994 disclose solder material alloys within the above described general field, which were especially developed for soldering aluminum-based alloys of the Al-Fe-V-Si type produced by powder metallurgy techniques. Those disclosed solder materials are provided in the form of thin foils that are arranged at the joints to be soldered.
Japanese Patent Document JP 62-38796, as summarized in the Patent Abstracts of Japan, M-609, Vol. 11, No. 225 (1987) discloses an aluminum-based solder material that may contain from 0.01 wt. % to 1 wt. % of indium. The solder alloy may contain no germanium at all, or up to 1 wt. % of germanium. However, in the alloy containing indium, the total content of indium and germanium together is limited to a maximum of 1 wt. %.